Preliminary Interpretation of the Ground Magnetic Survey Around Oguta Lake in Imo State, South Eastern Nigeria

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Preliminary Interpretation of the Ground Magnetic Survey around Oguta Lake in Imo State, South Eastern Nigeria

CHINYEM, F I

Department of Geology, Delta State University, Abraka, Delta State, Nigeria

ABSTRACT: Ground magnetic profiling was carried out around Oguta Lake in Imo State, Southeastern Nigeria. Seventy-Six stations in three profiles were established at five hundred meters intervals on major roads in the study area, A total distance of thirty five kilometers was covered. The result indicates that the highest field reading was 32835gamma while the lowest field was 28118gamma. Five anomalies were observed. The anomaly at the lake, was most prominent with magnetic readings of 28118 -29235 gamma and elevations of 17 -37 feet, all treading in the NE –SW direction. These anomalies, suggest that the lake has a tectonic origin. @JASEM

Keywords: Ground magnetic profiling, interpretation, Oguta Lake, Anomaly, Tectonic Origin

Lakes are basins formed by many geological The objective of this study therefore is to use ground processes such as buckling of stratified rock into magnetic profiling to map for geologic structures like large folds, displacement of large masses of rock by faults, fractures, ground Oguta Lake, as well as to fault, and blocking of valleys by landslides. Lakes are find out if the lake has a tectonic origin. also formed by glaciations, which weakens and removes the bedrock thereby forming depression. The Study Area: The study area lies between latitudes Huron superior lake in Canada and Finger Lake of 50 04 1 and 5 0 44 1 N of the Equator and longitude 6 0 New York are formed through this process (Monroe 41 1 and 6 0 60 1 East of the Greenwich meridian. The and Wicander, 2005). Lake water is gotten lake is linear in shape and fed by main rivers namely: through atmospheric precipitation that reaches the Njaba River and Awbana River. It has a surface and lake directly and by means of springs, brooks, and bottom current with velocities in the range of 20- rivers. Lakes form and disappear over the course of 140cms -1 and 10 – 19cms -1 respectively (Lozan, varying lengths of geological time. Lakes may 1979). It has a total surface area of 2.8km 2 and evaporate as the climate become arid, or they may be maximum depth in the dry/flood season ranges from filled up with sediments, leaving a bog or swamp in 7.0m to 9.0m with depth of 5.50m (Nwadiaro and the place. In arid regions, where precipitation is Umeham, 1985). Oguta Lake is located in the slight, lakes sometimes dry up for long period of northern tip of the lower Niger Delta. There are two time. In situations where evaporation prevents the major climatic seasons in the area, the wet season lake water from overflowing the basin rims, from April to October and dry one from November to substances dissolved in water becomes concentrated. March. Average annual rainfall is over 19.30mm The dissolved matter, brought by tributary streams (Akintola, 1986). The dry season is characterized by varies in composition with the nature of the rocks in high temperature and low humidity while the rainy the local drainage system. The primary mineral season has lower temperature and high relative constituent of salt lakes is common salt. Bitter lakes humidity. In average, temperature for the year in the contain sulphates, borax lakes contain borates, alkali area is 25 0 C. lakes contain carbonates, and some lakes contain combination of these substances. Lakes form at all The Geology: The geology of the area is well attitudes and are distributed throughout the world, documented (Reyment, 1965, Short and stanble, almost one half being in Canada. They are abundant 1967). Oguta and its adjacent environments fall in high attitudes, particularly in mountains ranges within the Northern of the Niger Delta. The surface subjected to glacial action. Many lakes are important geology in the study area is essentially the coastal commercially as sources of fish and minerals, plain sands – the Benin Formation (Mid – Eocene and shipping, holiday resort etc. The Capsian sea, Lakes Recent), the Sombreiro- Warri Deltaic plain and the superior and Victoria are the largest lakes in the Recent alluvial deposits. Benin Formation consists of world. The Dead sea is the lowest lake, 40 m below thick bodies of yellow (ferruginous) and white sands sea level. The Capsian sea is the world’s largest lake, which are friable, poorly sorted and intercalated with covering an area of 370,998 sqkm. Lake Baikal is the shale, clay tenses and lignite. Formation thickness deepest fresh water lake in the world, with a may be up to 200metres in some areas. Onyeagocha, maximum depth of 1,637m. (1980) reports that the Formation is overlain in many places by reddish lateritic material formed by in – situ Oguta Lake is one of the inland drainage basins of weathering and ferruginization of the rock. non-marine habitat, located on a low-lying continental plat form in southeastern Nigeria. It is the largest lake in southeastern Nigeria (Lozan, 1976).

Email : [email protected] 602 Preliminary Interpretation of the Ground Magnetic…...

MATERIALS AND METHODS were established for the second profile (P 2) and the A proton – precession magnetometer (G 816/ 826A total distance of 11.8km was covered. For the third model) was used for the data acquisition in which a profile (P 3), twenty five stations were established and leap frog method was used. Seventy six stations were a total distance of 11.5km was covered. The times as established in three profiles. The spacing interval well as the elevation (height above sea level) readings between stations was 500metres and the total distance were taken along side with the magnetometer covered was 35kilometres. For the first profile (P1), readings at each station as showed in tables 1, 2 and twenty five stations were established and a total 3. At an hour interval looping was carried out in order distance of 11.7km was covered. Twenty six stations to check for drift.

Table 2: Field data from Profile 2 (P 2): (Oguta Lake – Awo- Table 1: Field data from Profile 1(P 1): Izombe Sec. Community School – Oguta Lake, via Oguta STATION READING IN MEAN GAMMA STATION READING IN MEAN GAMMA P1B0 31697 31693 (BASE) 31697 P1A0 31549 31552 31685 31553 P1B1 31479 31517 31554 31495 P1A1 30691 29654 31577 29253 P1B2 31445 31522 29019 31467 P1A2 28042 28842 31655 29090 P1B3 31947 31929 29393 31946 P1A3 31653 31654 31875 31655 P1B4 32185 32532 31653 32947 P1A4 31659 31656 32465 31654 P1B5 30447 30458 31654 30443 P A 31135 31445 1 5 30485 31601 P1B6 31487 31480 31600 31487 P A 30667 31445 1 6 31467 30663 P1B7 28113 28118 30661 (200m) 28121 P1A7 30683 30682 28119 30684 P1B0 31177 31162 30680 (LOOP 31119 P1A8 30683 30682 31189 30683 P1A9 30697 31697 30683 30697 P1A9 30697 31697 30697 30697 P1A10 31175 31180 30697 31187 P1A10 31175 31180 31177 31187 P1A11 31685 31671 31177 31669 P1A11 31685 31671 31657 31669 P1A12 31675 31673 31657 31675 P1A12 31675 31673 31679 31675 P1A13 31551 31586 31679 31603 P1A13 31551 31586 31605 31603 P1A14 31527 31527 31605 31527 P1A14 31527 31527 31527

31527 P A 31343 31331 1 15 31527 31327

P1A15 31343 31331 31323

31327 P A 31454 31459 1 16 31323 31461

P1A16 31454 31459 31463 31461 P1A0 31345 31349 31463 Loop 31345 P1A0 31345 31349 31357 Loop 31345 31357

CHINYEM, F I

603 Preliminary Interpretation of the Ground Magnetic…...

STATION READING IN MEAN STATION READING IN MEAN GAMMA GAMMA P2B0 31073 31069 P2A0 30535 30604 (BASE) 31067 30635 31067 30643 P2B1 31857 31850 P2A1 32191 32129 31847 32194 31847 32002 P2B2 31689 31686 P2A2 31377 31375 31685 31374 31683 31374 P2B3 31817 31284 P2A3 31673 31667 31017 31674 31017 31654 P2B4 31675 31492 P2A4 31011 31011 31117 31017 31685 31005 P2B5 31067 31583 P2A5 30294 30253 31835 30221 31847 30244 P2B6 32227 32237 P2A6 31144 31145 32227 31143 32257 31147 P B 32117 32050 2 7 P2A7 31464 31465 32017 31467 32015

31464 P B 31544 31452 2 8 P2A8 32084 32069 31405

32059 31407

32065 P B 31403 31405 2 9 P2A9 31431 31432 31405

31434 31407 31431 P2B10 31115 31120 P A 31597 31635 2 10 31127 31679 31119 31629 P2B11 31997 31972 P A 31587 31586 2 11 31967 31575 31951 31597 P2B12 32441 32456 P A 31185 31178 2 12 300m 32867 31175 32059 31174 P2B0 31003 31052 P2A0 31003 31052 Loop 31075 (Loop) 31075 31077 31077

PROFILE 1 : T his profile runs in the NNE-SSW is characterized by Alluvium and Benin Formation direction and cut across the area where the geology is (Fig. 1). A total distance of 11.8km was covered and characterized by the Sombreiro- Warri Deltaic plain twenty six stations established. An anomaly was and Alluvium. Settlements that falls in this profile observed at stations 5 (Fig. 2) which is 2.3km from includes: Nnebuku, Izombe and Ossu-Obodo (Fig. 1). the lake. This corresponds with steep Twenty five stations were covered at a total distance slope/depression in Oguta main town. An uneven of 11.7km. Anomalies were observed at station 2 magnetic value was observed as one moves away (Fig. 2) which is 1km from the base station (Izombe) from the lake. This may be as a result of intercalation as well as at stations 6, 7 and 8. There was a high of sand and shale in the area. uniform magnetization between stations 10 and 20. This area is mainly alluvium, which is characteristic PROFILE 3 : The profile runs in NNW-SSE direction of clay, shale, silt sand and gravels that have high and cuts across Mgbidi and Awomamma settlements adsorption capacity of heavy minerals. There was a where the geology is characterized by alluvium. A sharp drop or plunge between stations 22 and 24 total distance of 11.5km was covered and twenty five which are close to the lake. The last station having stations were established. This profile is characterized the lowest magnetic value of 28118gamma, which is by magnetic values as high as 32838 gamma. 17ft above sea level can be said to be as a result of Generally, there was variation in magnetization in depression or tectonic activities. this profile (Fig. 3). It was observed from the alignment of profiles 1 and 2 that there was a sharp PROFILE 2: The profile runs in the NNW – SSE plunge at the last station of profile 1 and the first direction and cuts across the area where the geology station of profile 2, which are both on the Oguta lake

CHINYEM, F I

604 Preliminary Interpretation of the Ground Magnetic…... axis. This is a clearer indication of a fault within that region.

Table 3: Field data from Profile 3 (P 3): (Awo-Omama/Mgbidi Junction - Obumiri) Base Station (A): Awo-Omama/Mgbidi Junction Base Station (B) A B

STATION READING MEAN STATION READING IN MEAN IN GAMMA GAMMA

P2A0 30447 29924 P3B0 31137 31383 (BASE) 29271 (BASE) 31187 30054 31824 P3A1 32197 31825 P3B1 35491 32000 31674 36125 31605 36415 P3A2 30625 30328 P3B2 31837 31827 30509 31827

29851 31817

P3A3 31197 31190 P3B3 31191 31192 31179 31185 31193 31199

P3A4 31163 31544 P3B4 31825 31832 31817 31825 31653 31847 P3A5 31183 31160 P3B5 32312 32303 31119 32315 31179 32281 P3A6 32071 31988 P3B6 32133 32139 31885 32117 32007 32167 P3A7 32833 32838 P3B7 31887 31863 32843 31814 32837 31887 P3A8 31193 31164 P3B8 31203 31208 31154 31197 31145 31224 P3A9 31329 31364 P3B9 30163 30149 31379 30167 31385 30117 P3A10 32585 32502 P3B10 31007 31130 32483 31187 32437 31195 P3A11 30957 30961 P3B11 31997 31972 30973 31967 30954 31951

P3A12 31123 31128 P3B0 31997 31654 31125 Loop 31475 31137 31491 P3A13 31864 31859 31877 31837

P3A0 31817 31833 (Loop) 31874 31807

CHINYEM, F I

605 Preliminary Interpretation of the Ground Magnetic…...

PROFILE 1 (IZOMBE SEC. SCH. - OGUTA LAKE, OGUTA 2) 33000 32000 31000 30000 29000 28000 27000 0 5 10 15 20 25 30

Station interval = 500m (m) Meab Field Value (in Gamma) (in ValueField Meab

Fig. 1: Profile 1 (Izombe Sec. Sch. - Oguta Lake, Oguta 2

Profile 2 (Oguta Lake, Oguta 1 - Awo Omama/Mgbidi Junction ) 33000 32500 32000 31500 31000 30500

Gamma) 30000 0 5 10 15 20 25 30

Mean Field Value (in FieldValue Mean Station interval = 500m stations (m)

Fig. 2: Profile 2 (Oguta Lake, Oguta 1 – Awo-Omama/Mgbidi Junction)

Profile 3 (Awo Omama/Mgbidi Junction-Obumiri) 33000

32500

32000

31500

31000

30500

30000

Mean Field Value (in gamma) FieldValue Mean 29500 0 5 10 15 20 25 30

Station interval = 500m Stations (m)

Fig. 3: Profile 3 (Awo-Omama/Mgbidi Junction - Ubomiri

CHINYEM, F I

Conclusion: This research work has achieved some Ananaba, S. E and Okereke, C . N (2006). Deep level of success in the use of ground magnetic crustal lineament inferred from acromagnetic profiling to map for geologic structures like faults, anomalies over the Niger Delta. Journal of mining fractures and lineaments around Oguta Lake as well and geology, 42(2): 127-131. as to find out if the lake has a tectonic origin. The ground magnetic profiling in the study area shows Lozan , C. (1976). Preliminary study of the anomalies which are characterized by low amplitudes possibility of using Oguta lake as a port. A report to and low relief. These anomalies are predominantly the Government of East Central State, 86p. due to basement lithology rather than topography. The signatures of the observed magnetic lineament Monroe , J. S. and Wicander, R. (2005). Physical trending in the NE – SW direction suggests that Geology, 5 th edition, Thompson Learning Inc. USA. Oguta lake considering its co-ordination falls within the charcot fracture zone. It is therefore Nwadiaro, C. S. and Umeham, S.N. (1985). The recommended that more ground magnetic profiling chemical hydrology of Oguta Lake , Imo State, South should be done in other directions that were not Eastern Nigerian, Arch. Hydrobiology, 103 (2): 251- covered during the course of this work so as to 267 authenticate this proof. It is equally recommended that an aeromagenetic survey of Oguta lake and its Onyeagocha, A. C. (1980). Petrology and environs be done so as to confirm the presence of depositional environment of the Benin Formation. geologic structures as well as the depression at the Journal of Mining and Geology, 17:147-151. lake. Reyment, R .A. (1965). Aspects of the Geology of REFERENCES Nigeria, Ibadan university press . 145p. Akintola , J. O. (1986). Rainfall distribution in Nigeria, 1892-1983. Impact publishers Nig. Ltd; Short , K. C. and Stauble, A. J. (1967). Outline of Ibadan, 380p Geology of Niger Delta, AAPG Bull. 51: 7661-799.

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